In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers (248 nm) are the main light source used in mass production, and ArF excimer lasers (193 nm) are now also starting to be introduced in mass production.
Resists for use with light sources such as KrF excimer lasers and ArF excimer lasers require a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity relative to light sources with this type of short wavelength. One example of a known resist that satisfies these conditions is a chemically amplified positive resist composition which includes a base resin that exhibits increased alkali solubility under the action of acid, and an acid generator (hereafter referred to as a PAG) that generates acid on exposure.
In the reaction mechanism of a chemically amplified positive resist, exposure causes the PAG within the resist to generate an acid, and this acid causes a change in the solubility of the base resin. For example, if dissolution-inhibiting groups that eliminate in the presence of acid are introduced into the base resin of the chemically amplified positive resist, then these dissolution-inhibiting groups will eliminate only within the exposed portions of the resist, causing a significant increase in the solubility of the resist in the developing solution within these exposed portions. Typically, by conducting a heat treatment following exposure (post exposure baking, hereafter abbreviated as PEB), the dissociation of the dissolution-inhibiting groups and the elimination of the acid within the resist is accelerated, enabling a much higher sensitivity to be achieved than that attainable with conventional non-chemically amplified resists.
Moreover recently, the design rules prescribed for semiconductor element production have become even more stringent, and for example, resist materials with resolution levels capable of forming a resist pattern of 130 nm or less using an ArF excimer laser (193 nm) are now being demanded. In order to meet these demands for miniaturization, the development of resist materials capable of forming very fine resist patterns using an ArF excimer laser is being vigorously pursued.
Until recently, polyhydroxystyrenes or derivatives thereof in which the hydroxyl groups are protected with acid-dissociable, dissolution-inhibiting groups (hereafter also referred to as hydroxystyrene-based resins), which exhibit high transparency relative to a KrF excimer laser (248 nm), have been used as the base resin component of chemically amplified resists.
However, resins such as hydroxystyrene-based resins that contain benzene rings have insufficient transparency in the vicinity of 193 nm. As a result, chemically amplified resists that use these resins as a base resin suffer from lower levels of resolution.
Accordingly, resist compositions that employ a resin that contains, within the principal chain, structural units derived from a (meth)acrylate ester containing a polycyclic hydrocarbon group such as an adamantane skeleton at the ester portion (for example, see patent references 1 through 8) as the base resin have been proposed as resist materials that contain no benzene rings, exhibit excellent transparency in the vicinity of 193 nm, and also exhibit superior dry etching resistance.
However, the polymer that functions as the base resin component within these types of chemically amplified photoresist compositions is obtained by radical polymerization of a plurality of (meth)acrylate ester monomers. Unfortunately, the molecular weight distribution of a polymer obtained by such radical polymerization exceeds 1.5, which can cause problems such as an inability to adequately control the molecular weight and a low yield.
On the other hand, Japanese Unexamined Patent Application, First Publication No. 2003-84436 (patent reference 9) has proposed a resist that uses a polymer for which the molecular weight distribution is 1.5.
(Patent Reference 1)
Japanese Patent (Granted) Publication No. 2,881,969
(Patent Reference 2)
Japanese Unexamined Patent Application, First Publication No. Hei 5-346668
(Patent Reference 3)
Japanese Unexamined Patent Application, First Publication No. Hei 7-234511
(Patent Reference 4)
Japanese Unexamined Patent Application, First Publication No. Hei 9-73173
(Patent Reference 5)
Japanese Unexamined Patent Application, First Publication No. Hei 9-90637
(Patent Reference 6)
Japanese Unexamined Patent Application, First Publication No. Hei 10-161313
(Patent Reference 7)
Japanese Unexamined Patent Application, First Publication No. Hei 10-319595
(Patent Reference 8)
Japanese Unexamined Patent Application, First Publication No. Hei 11-12326
(Patent Reference 9)
Japanese Unexamined Patent Application, First Publication No. 2003-84436